US7256384B2 - Signal-enhancement system for photodetector outputs - Google Patents

Signal-enhancement system for photodetector outputs Download PDF

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US7256384B2
US7256384B2 US11/255,875 US25587505A US7256384B2 US 7256384 B2 US7256384 B2 US 7256384B2 US 25587505 A US25587505 A US 25587505A US 7256384 B2 US7256384 B2 US 7256384B2
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filter
volts
amplifier
digital
signal
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US20060086891A1 (en
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Tal Gottesman
Bernard J. Mcgee
Vikram A. Bose-Mullick
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
    • H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
    • H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
    • H03F3/087—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light with IC amplifier blocks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
    • H03F3/45928—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit
    • H03F3/45968—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit by offset reduction
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/68—Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3084—Automatic control in amplifiers having semiconductor devices in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/261—Amplifier which being suitable for instrumentation applications

Definitions

  • the field of the invention is signal enhancement of photo detector outputs as seen, for example, in aerosol particle detection and measurement systems.
  • the present invention is related to enhancement of electrical signals for the detection of light detected by a photodiode and more specifically by light detected by a photodiode as the result of light scattering from a concentration of aerosol particles.
  • photodetectors examples include, but are not limited to, optical character recognition systems, communication systems medical imaging sensors, laser range finders, radiation detectors, smoke detectors, position sensors and proximity sensors.
  • a photodetector is used to measure light or radiation in terms of an electrical signal that is processed in various ways to produce a useful information output.
  • a beam of collimated light which may or may not be coherent, is directed through a transparent cell in which particles suspended in fluid mixtures are made to pass.
  • Photodetectors are then used to detect the relative amount of light that is scattered or blocked by the particles.
  • the signals generated by the photodetector contain information about the concentration of particles, size of particles, and/or presence of particles.
  • photodetector depends on the sensitivity requirements of the device.
  • a photo-multiplier tube is the most sensitive (and costly) method that is currently available.
  • a photo-multiplier can detect the presence of a single photon with nanosecond resolution.
  • photo-multiplier tubes are very costly to manufacture and are easily damaged. Additionally they have very high voltage requirements and therefore tend to be used in laboratories rather than in commercial applications.
  • photo-multiplier tube One alternative to using a photo-multiplier tube is to use a photodiode and a transimpedance amplifier. In contrast to a photo-multiplier, photodiodes are inexpensive, rugged, small, and operate at low voltages.
  • Another background art device that is used to measure aerosol particle size and concentration is called a light scattering photometer or nephelometer.
  • Applications that require particularly sensitive measurements require photo-multiplier-based photometers.
  • a photodiode-based device When the sensitivity requirements of the application do not justify the use of a photo-multiplier tube, a photodiode-based device is preferred due to the reduced cost.
  • background art photodiodes are not as sensitive as photo-multiplier tubes and are prone to noise problems associated with electrical amplification.
  • the sensitivity of a photodiode device is in part a function of the gain of a transimpedance amplifier associated with the photodiode device.
  • the amplified signals contain useful information pertaining to the amount of light reaching the photo detector.
  • the amplified signal also contains additional factors such as offset voltage potential, noise generated by ambient light and electromagnetic interference. These additional factors have the effect of limiting the possible gain of the amplifier stages before reaching saturation. Therefore, there is a need in the art for a low-cost photodiode-based detector with improved gain and sensitivity.
  • the present invention is an apparatus and method for amplification, filtering, DC cancellation, and signal processing of photodetector output signals in order to extract useful information related to the amount of light reaching the detector.
  • Examples of photodetectors include, but are not limited to, photodiodes, phototransistors, photomultiplier tubes and Charge Coupled Device (CCD) image sensors.
  • the present invention also provides a means for outputting the useful information extracted from the photodetectors via at least one of a serial link, visual display, analog output, radio link, or audio output.
  • the gain and sensitivity of a photodiode-based detector is increased by at least removing the noise and DC offset. This increased sensitivity allows the photodiode-based detector of the present invention to be used in applications that currently require a photo-multiplier-based photometer.
  • One embodiment of the present invention is an apparatus for enhancing electronic signals from a photodetector comprising: an amplifier; a clamp circuit connected to the amplifier; a programmable gain amplifier connected to the clamp circuit; filter connected to the programmable gain amplifier; a notch filter connected to the filter; an analog-to-digital converter connected to the notch filter; at least one digital-to-analog converter connected to the analog-to-digital converter; an inverting-summing amplifier; an input of the amplifier; at least one DC reference generator; and a computer, wherein the computer is connected to the analog-to-digital converter, the programmable gain amplifier, the filter, the notch filter and the at least one digital-to-analog converter and provides feedback control and digital filtering for the apparatus.
  • Another embodiment of the present invention is a method for enhancing electronic signals from a photodetector comprising: at least one of starting and resetting the photodetector; initializing digital-to-analog converters (DACs), analog-to-digital converters (ADCs) programmable gain amplifiers (PGAs) and filter parameters; subtracting a voltage increment from the output of a filter until the output of the filter is at least one of less than and equal to a predetermined coarse threshold voltage; subtracting a voltage increment from the output of the filter until the output of the filter is at least one of less than and equal to a predetermined fine threshold voltage; filtering and signal processing the output of the filter; and outputting the filtered and signal processed output of the filter until receiving at least one of a power down and reset command.
  • DACs digital-to-analog converters
  • ADCs analog-to-digital converters
  • PGAs programmable gain amplifiers
  • FIG. 1 is an exemplary block diagram showing the functional blocks used to implement the apparatus and method of the present invention.
  • FIG. 2 is an exemplary flowchart showing the photometer signal auto zeroing via an adaptive DC cancellation algorithm.
  • FIG. 1 shows the apparatus of the present invention.
  • FIG. 1 shows an example of the functions of amplification, filtering, DC-cancellation, and signal processing of a photometer device.
  • the analog signal from the photometer is input into the apparatus via a twisted pair cable connected to the non-inverting input of an instrumentation amplifier 1 .
  • the amplifier 1 can be any type of instrumentation amplifier and should be selected with a high common mode rejection ratio (CMRR) as the major deciding factor.
  • CMRR common mode rejection ratio
  • the amplifier 1 should ideally have a CMRR of at least 85 dB.
  • This amplifier 1 in the system can also provide a small gain to the signal (i.e., between 1 and 10).
  • the output of the instrumentation amplifier 1 may then pass through a voltage clamp 2 to protect the rest of the system from over-voltage or under-voltage signals.
  • the analog signal After passing through the voltage clamp 2 , the analog signal passes through at least one programmable gain amplifier (PGA) 3 that further amplifies the signal.
  • PGA programmable gain amplifier
  • the exact gain of the PGA 3 is controlled by the microcontroller (MCU) 7 , and can be programmed to suit the specific application. In addition, the gain may be static or a function of a control algorithm.
  • the signal is then filtered with a low pass filter 4 with a cutoff frequency that may be fixed or controlled by the MCU 7 .
  • the low pass filter 4 may be passive or active and may be activated or deactivated by the MCU 7 , or bypassed with the use of a jumper.
  • a notch filter 5 is then implemented to remove frequency specific noise in the signal.
  • the stop band of the notch filter 5 has a default frequency of 60 HZ, and can be shifted by the MCU 7 or with settings determined by jumpers.
  • the notch filter 5 may also be passive or active, and may be bypassed by the MCU 7 or with the use of a jumper.
  • the output of the PGA 3 and filter blocks 4 , 5 may be provided as an analog output 11 of the apparatus.
  • the MCU 7 will receive this filtered signal after the filtered signal passes through an internal or external analog-to-digital converter (ADC) 6 .
  • the MCU 7 will also control several digital to analog converters (DACs) 8 , 9 , which may be internal or external to the MCU 7 .
  • DACs digital to analog converters
  • the voltage references of the DAC blocks may be set so that each one is lower than a previous voltage reference. This configuration allows for a course adjustment DAC 8 , and successively finer adjustments DAC 9 .
  • An inverting summing amplifier 10 is used to sum and invert the outputs of one or more DACs 8 , 9 . This inverted sum is then input to the instrumentation amplifier 1 to create a negative DC offset for DC signal cancellation.
  • another DAC may be included in the output block 11 and would be controlled by the MCU 7 .
  • This enables the MCU 7 to implement a multitude of digital filtering techniques and to output the result as an analog voltage.
  • the MCU 7 can also control an internal or external serial port or other device for serial output. Any number of other output devices may be driven by the MCU 7 to provide an audio output, visual display, or radio link output.
  • the photodetector has a maximum sensitivity having an approximate wavelength of between at least one of 100 and 400 nm, 400 and 600 nm, 600 and 700 nm, 700 and 1100 nm for the ultra violet spectrum, blue-green-yellow spectrum, red spectrum, and infrared spectrum, respectively.
  • a signal from the photodetector is amplified via a trans-impedance amplifier to achieve a gain of between at least one of 1 and 30,000; 1 and 10,000,000, wherein the amplifier has a common mode amplification is achieved from an instrumentation amplifier with a high Common Mode Rejection Ratio (CMRR) and a gain of 5.
  • CMRR Common Mode Rejection Ratio
  • the instrumentation amplifier preferably has at least one of a common mode amplification gain that is variable between at least one of 1 and 100; a common mode amplification gain that is fixed between 1 and 100.
  • the programmable gain amplifier cascade is preferably dynamically controlled by the computer; and the programmable gain amplifier achieves a gain of between at least one of 1 and 30,000; and 1 and 100,000.
  • the filter preferably provides band compensation; an anti-aliasing signal used for digital processing.
  • the filter is preferably configured to provide at least one of a Butterworth response, a Bessel response, a Chebychev Response, and an Elliptic response.
  • the filter is between 1st and 8th order, at least one of passive and active, at least one of a continuous time filter and a switched capacitor, and implemented as a digital filter.
  • the notch filter is preferably designed for at least one of a 60 Hz cut-off and a 50 Hz cut-off, at least one of an active filter and a passive filter, and at least on of a continuous time filter, digital filter and a switched capacitor filter.
  • the computer is configured to estimate the DC noise and to utilize a feedback control scheme for canceling the DC noise; measures the amplified signal via an analog-to-digital Converter; measures the amplified signal via a voltage comparator; controls a DC reference generator for subtracting an initial input DC offset voltage using a closed loop feedback scheme; controls at least one of an audio alarm, visual display, machine interlock, and radio transmitter; generates a DC level via Digital-to-Analog Converter for subtracting an input DC offset voltage with a closed loop feedback scheme; generates a DC level via a buffered digital potentiometer for subtracting an input DC offset voltage with a closed loop feedback scheme; generates a DC level via pulse width modulation for subtracting an input DC offset voltage with a closed loop feedback scheme; and provides various digital and analog outputs to control the components that comprise the apparatus.
  • the analog output may range between at least one of 0 and 5 volts, 0 and 1 volts, 0 and 10 volts, 0 and 12 volts, 0 and 3.3 volts, and 0 and 24 volts; and the apparatus is powered by a DC source of at least one of 5 Volts, 3.7 Volts, 7.4 Volts, 3.3 Volts, 9 Volts, 12 Volts, 24 Volts, 110 Volts, and 220 Volts.
  • step 21 of FIG. 2 is directed to an initial step of powering or resetting the system.
  • the MCU After power-up or when reset, the MCU initializes the hardware of the system, as shown in step 22 .
  • step 22 at least comprises setting the output voltages of the DACs to 0V; setting the PGA gain to zero; initializing the ADCs; and setting the corner frequencies of the filters.
  • step 23 the MCU runs the Coarse Sample and Subtract Loop.
  • the MCU reads the voltage level of the output signal of the filter blocks, via the ADC value.
  • Step 23 B determines whether the voltage level is above a predetermined coarse threshold voltage level.
  • step 23 C If the voltage level of the output signal of the filter blocks is above the predetermined coarse threshold voltage level (i.e., “YES” output for 23 B), then a coarse adjustment is made in step 23 C where the MCU increments coarse DAC voltage. Step 23 C has the effect of subtracting the incremented voltage from the output signal. Steps 23 A, 23 B and 23 C are repeated until the DC component of the input signal has been canceled to within the predetermined coarse threshold voltage level. When the voltage level is within the predetermined coarse threshold voltage level (i.e., “NO” output for 23 B), the method continues to the Fine Sample and Subtract Loop 24 , as shown in FIG. 2 .
  • step 24 A the MCU reads the voltage level of the output signal of the filter blocks, via the ADC value.
  • Step 24 B determines whether the voltage level is above a predetermined fine threshold voltage level.
  • step 24 C If the voltage level of the output signal of the filter blocks is above the predetermined fine threshold voltage level (i.e., “YES” output for 24 B) then a fine adjustment is made in step 24 C, where the MCU increments fine DAC voltage. Step 24 C has the effect of subtracting the incremented voltage from the output signal. Steps 24 A, 24 B and 24 C are repeated until the DC component of the input signal has been canceled to within the predetermined fine threshold voltage level. Until the output voltage is less than the predetermined fine threshold voltage. There may be as many successively finer DAC adjustments and threshold voltages as a specific application demands. When the voltage level is within the predetermined fine threshold voltage level (i.e., “NO” output for 24 B), the method continues to the Sampling/Processing section 25 , as shown in FIG. 2 .
  • Step 25 of FIG. 2 shows the Sampling/Processing Loop 25 .
  • the MCU will continuously sample the filtered signal via the ADC in step 25 A. Sampling is performed by the ADC at regular time intervals in accordance with the Nyquist sampling theorem (i.e., at least two (2) times the highest frequency component).
  • the MCU may then implement any number of digital filtering, pattern recognition, or predictive control algorithms in the Digital Filtering and Signal Processing functions of step 25 B.
  • Non-limiting examples of such algorithms include Proportional Integral, Least Mean Square or Kalman Filter.
  • the MCU outputs the results via at least one of an output DAC, serial output port, parallel output port, USB output port and Radio Link before continuously repeating the Sampling/Processing Loop 25 .
  • the MCU may also control specific output devices such as an audio alarm, visual display, machine interlock, radio transmitter, or any other electrically controlled device.
  • the Sampling/Processing Loop 25 will continue until either the device is powered down or reset by the user or by the MCU in response to a preprogrammed condition.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Amplifiers (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Spectrometry And Color Measurement (AREA)
US11/255,875 2004-10-22 2005-10-24 Signal-enhancement system for photodetector outputs Expired - Fee Related US7256384B2 (en)

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US11/775,515 US20080135735A1 (en) 2004-10-22 2007-07-10 Signal-enhancement system for photodetector outputs

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US20080075449A1 (en) * 2006-09-26 2008-03-27 Lee Sang Y Auto Exposure Controlling Device and Method
US7453230B1 (en) * 2006-09-29 2008-11-18 Cypress Semiconductor Corp. Synchronization circuit and method of performing synchronization
US20090219091A1 (en) * 2008-02-28 2009-09-03 Mccawley Michael System and method for measuring the output of a photodetector
US20100026535A1 (en) * 2008-08-04 2010-02-04 Honeywell International Inc. Segmented optics circuit drive for closed loop fiber optic sensors
US20120133406A1 (en) * 2010-11-30 2012-05-31 Infineon Technologies Ag Configurable System for Cancellation of the Mean Value of a Modulated Signal
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US7859577B2 (en) * 2006-09-26 2010-12-28 Lg Innotek Co., Ltd. Auto exposure controlling device and method
US8411163B2 (en) 2006-09-26 2013-04-02 Lg Innotek Co., Ltd. Auto exposure controlling device and method
US20080075449A1 (en) * 2006-09-26 2008-03-27 Lee Sang Y Auto Exposure Controlling Device and Method
US20110058066A1 (en) * 2006-09-26 2011-03-10 Lg Innotek Co., Ltd. Auto exposure controlling device and method
US7453230B1 (en) * 2006-09-29 2008-11-18 Cypress Semiconductor Corp. Synchronization circuit and method of performing synchronization
US20090219091A1 (en) * 2008-02-28 2009-09-03 Mccawley Michael System and method for measuring the output of a photodetector
US7732749B2 (en) 2008-02-28 2010-06-08 Respiratory Management Technology System and method for measuring the output of a photodetector and for reducing sensitivity to temperature variations
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US20100026535A1 (en) * 2008-08-04 2010-02-04 Honeywell International Inc. Segmented optics circuit drive for closed loop fiber optic sensors
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US20060086891A1 (en) 2006-04-27
JP2008518211A (ja) 2008-05-29
US20080135735A1 (en) 2008-06-12
WO2006047473A2 (en) 2006-05-04
WO2006047473A3 (en) 2006-12-07
AU2005299470A1 (en) 2006-05-04
MX2007006054A (es) 2008-02-21
CA2585016A1 (en) 2006-05-04
EP1807930A2 (de) 2007-07-18

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